Should my contractor strip my flat roof before EPDM?

[Jordan Kim]

I have a duplex with a flat roof - Tar and gravel - I'm looking to have it replaced before next winter and have had one contractor say that he could drill insulation board right on top of the existing roof and cover that with the EPDM membrane. 

My question is whether anyone has an opinion on if stripping the roof of the tar and gravel layer would be beneficial from a weight-bearing standpoint? I live in a snowy climate and in my mind, stripping it would make the roof considerably lighter - or does it not matter? 

Thanks for anyone's opinion who has roofing experience! 

[Joel Owens]

I have seen before if the roof gets too many layers or weight then might not meet county or city codes and insurance company denies insuring the whole building.